This application relates generally to disc drives and more particularly to a clamping mechanism for retaining one or more data storage disc on a spin motor.
Disc drives are data storage devices that store digital data in magnetic form on a rotating storage medium on a disc. Modern disc drives comprise one or more rigid discs that are typically coated with a magnetizable medium and mounted on the hub of a spin motor for rotation at a constant high speed. Information is stored on the discs in a plurality of concentric circular tracks typically by transducers (xe2x80x9cheadsxe2x80x9d) mounted to an actuator assembly for movement of the heads relative to the discs. During a write operation, data is written onto the disc track and during a read operation the head senses the data previously written on the disc track and transfers the information to the external environment. Critical to both of these operations is the accurate positioning of the head over the center of the desired track.
The heads are each mounted via flexures at the ends of actuator arms that project radially outward from the actuator body or xe2x80x9cExe2x80x9d block. The actuator body typically pivots about a shaft mounted to the disc drive housing adjacent to the outer extreme of the discs. The pivot shaft is parallel to the axis of rotation of the spin motor and the discs, so that the heads move in a plane parallel to the surfaces of the discs.
Typically, such actuator assemblies employ a voice coil motor to position the heads with respect to the disc surfaces. The voice coil motor typically includes a flat coil mounted horizontally on the side of the actuator body opposite the actuator arms. The coil is immersed in a vertical magnetic field of a magnetic circuit comprising one or more permanent magnets and vertically spaced apart magnetically permeable pole pieces. When controlled direct current (DC) is passed through the coil, an electromagnetic field is set up which interacts with the magnetic field of the magnetic circuit to cause the coil to move in accordance with the well-known Lorentz relationship. As the coil moves, the actuator body pivots about the pivot shaft and the heads move across the disc surfaces. The actuator thus allows the head to move back and forth in an arcuate fashion between an inner radius and an outer radius of the discs.
Modern disc drives typically include one or more discs mounted to the spin motor. Spacers are used to provide the separation between discs necessary for the actuators arms to movably locate the heads in relation with the disc surfaces. The discs and spacers collectively form a disc stack assembly, or disc pack, that is mounted on the spin motor hub and held together with a leaf spring disc clamp.
Disc clamps can be either stamped or milled. While milled clamps are more rigid and less prone to deflecting the abutting disc surface, they are relatively expensive to produce. Consequently, stamped leaf spring disc clamps, which are substantially less expensive, have become popular. The clamp is typically a circular spring-steel, sheet metal structure having a central portion and a rib portion at or near the outside diameter of the clamp, with an annular rib formed in the rim portion of the clamp. The central portion of the leaf spring disc clamp has a partial aperture that is bent or deflected toward the center of the clamp, forming a leaf spring above the level of the annular rib, and includes a plurality of screw holes spaced symmetrically about the central portion of the clamp. The screws used to mount the disc clamp springingly bend and deflect the central portion of the clamp toward the upper surface of the motor spindle as the screws are tightened, thereby forcing the annular rib into firm contact with the uppermost disc surface and applying a clamping force to the disc stack.
This type of disc clamp is not without problems. The disc clamp is secured with a plurality of screws, typically 3, circumferentially spaced around the center of the clamp. The majority of the clamping force is exerted by the rib portion adjacent the screw locations, with a significantly reduced level of clamping force, and often no clamping force at all, exerted by the rib portion between the screw locations. This variation in clamping force can mechanically distort the discs in a phenomenon sometimes referred to as xe2x80x9cpotato chipping,xe2x80x9d meaning that the portions of the disc nearest the clamp screws are displaced further than the portions of the disc between the screws.
Disc drives are subject to external shocks and must be designed to meet certain specified shock requirements. The non-uniform clamping force from current disc clamp design requires higher clamping forces to prevent disc slip from external shocks to the disc drive and the higher clamping forces increase the severity of xe2x80x9cpotato chipping.xe2x80x9d
One solution to xe2x80x9cpotato chippingxe2x80x9d is to increase the number of mounting screws used to secure the disc clamp to the spin motor hub. As more screws are used and are spaced closer together, the discrepancy in clamping force is reduced but not eliminated. A disadvantage of this approach is that the use of additional screws complicates the manufacturing and assembly process and increases costs.
Mechanical distortion of the disc surface can, in turn, lead to undesirable variations in the read/write signals detected and written by the heads of the disc drive. Since the heads will fly at varying heights around the circumference of the disc while attempting to follow a distorted disc, the signals used to read and write data on the discs may be inadequate to ensure reliable data storage and recovery.
Another problem encountered with the current disc clamps is the transfer of vibrations from the discs to the clamp. Current disc clamps do not dampen vibrations from shocks to the disc drive and the vibrations can resonate in the disc clamp or set it to xe2x80x9cringing.xe2x80x9d This xe2x80x9cringingxe2x80x9d then is transferred to the discs. Vibrations in the discs are an additional source of undesirable variations in the read/write signals detected and written by the heads.
Accordingly there is a need for a mechanism that would more evenly distribute the force applied to the disc surface from the disc clamp and also dampen vibrations in the disc clamp.
Against this backdrop the present invention has been developed. The performance of a disc clamp can be enhanced by utilizing a roughly triangular shape for the center aperture. Such a disc clamp exhibits a substantially more uniform distribution of clamping force and reduces the xe2x80x9cpotato chippingxe2x80x9d of the disc. It has further been determined that a stiffening rib located adjacent to the rim portion which contacts the data disc also leads to more uniform distribution of clamping force. The invention has advantages over other mechanisms in that it does not require additional screws, other parts, or a significant change in the manufacturing process.
Accordingly, an aspect of the invention is found in utilizing a roughly triangular shaped central aperture in a disc clamp fastened with three screws to distribute the clamping force more uniformly on the disc.
Another aspect of the invention is providing a stiffening rib adjacent to the annular contract surface to increase the stiffness of the contact surface and more uniformly distribute the clamping force.
Yet another aspect of the invention is fastening a dampening ring to the disc clamp to reduce the amount of vibration in the disc clamp.
These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.